Spin Resistant Aircraft Configuration

ABSTRACT

A configuration and system for rendering an aircraft spin resistant is disclosed. Resistance of the aircraft to spinning is accomplished by constraining a stall cell to a wing region adjacent to the fuselage and distant from the wing tip. Wing features that facilitate this constraint include but are not limited to one or more cuffs, stall strips, vortex generators, wing twists, wing sweeps and horizontal stabilizers. Alone or in combination, aircraft configuration features embodied by the present invention render the aircraft spin resistant by constraining the stall cell, which allows control surfaces of the aircraft to remain operational to control the aircraft.

RELATED APPLICATION

The present application relates to and claims the benefit of priority toU.S. Provisional Patent Application No. 61/674,267 filed Jul. 20, 2012,which is hereby incorporated by reference in its entirety for allpurposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate, in general, to aerodynamictechniques designed to deter an aircraft's ability to enter a spin andmore particularly to a configuration of said techniques that renders anaircraft spin resistant.

2. Relevant Background

The primary cause of fatal accidents in small aircraft is loss ofcontrol. Loss of control usually occurs because the aircraft enters aflight regime that is outside its normal envelope usually, but notalways, at a high rate, thereby introducing an element of surprise forthe flight crew. Factors leading to a loss of control are many includingloss of situational awareness especially through distraction and/orcomplacency, intended or unintended mishandling of the aircraft,attempting to maneuver an aircraft outside its capabilities to resolve aprior problem, and the like. While every out of control situation isunique, one loss of control flight regime that every pilot it taught toavoid is a spin.

In aviation, a spin is an aggravated stall resulting in autorotationabout a spin axis wherein the aircraft follows a corkscrew downwardpath. Stalls in fixed-wing flight are often experienced as a suddenreduction in lift as the pilot increases angle of attack and exceeds thecritical angle of attack (which may be due to slowing down below stallspeed in level flight). Spins can be entered intentionally orunintentionally, from any flight attitude and from practically anyairspeed—all that is required is a sufficient amount of yaw (rotationabout a vertical axis) while an aircraft is stalled. In either case,however, a specific and often counterintuitive set of actions may beneeded for an effective recovery to be made. If the aircraft exceedspublished limitations regarding spins, or is loaded improperly, or ifthe pilot uses incorrect techniques to recover, the spin can, and oftendoes, lead to a crash.

In a spin, both wings are in a stalled condition, but one wing will bein a deeper stall condition than the other. This causes the aircraft toautorotate (yaw) towards the deeper-stalled wing due to its higher drag.At the same time, the wings produce an unbalanced amount of lift causingthe aircraft to roll and similarly adjust its pitch. An autorotation orspin is thus a stalled condition in which there is simultaneous movementaround all three aircraft axes—that is, yaw, pitch, and roll. And asmentioned, a spin results in a vertical flight path. That is to say theaircraft is falling directly to the earth as it spins.

FIG. 1 is a high level depiction of the interaction of aerodynamicforces acting on a wing going into a spin as is known by one ofreasonable skill in the relevant art. For discussion purposes, the wing100 is divided into two portions designated by the direction the wingportion will go in a spin. In this particular illustration, there is adown-going wing portion 110 and an up-going wing portion 120. For anaircraft to spin, the wing must be stalled. In this example, the wing100 is experiencing an angle of attack that is greater than the criticalangle of attack and thus, a stalled condition results. Here both thedown-going wing portion 110 and the up-going wing portion 120 areexperiencing a stalled condition. However in this case, the down-goingwing portion 110 possesses an angle of attack of 40 degrees 130 whilethe up-going wing portion 120 has an angle of attack of 25 degrees 135.The angle of attack of both wing portions 110, 120 exceeds the criticalangle and are both stalled, yet the stall is not symmetrical. As thedown-going wing portion 110 has a higher angle of attack 130, it willgenerate more drag 140 and less lift 150 than, comparatively, the drag145 and the lift 155 of the up-going wing portion 120. The unbalancedforces result in the wing 100 yawing 160 and rolling 170 simultaneously.

Spins, typified by an excessive angle of attack and slow airspeed,differ from spiral dives which are characterized by low angle of attackand high airspeed. In a spiral dive, the airplane will respondconventionally to the pilot's inputs to the flight controls whereas in aspin, the aircraft's response to flight controls is compromised.

Some aircraft cannot be recovered from a spin using only their ownflight control surfaces. Accordingly, if an aircraft has not beencertified for spin recovery, it is assumed that spins are notrecoverable and engaging in a spin is considered unsafe in thataircraft. For safety, all certificated, single-engine fixed-wingaircraft, including certificated gliders, must meet specified criteriaregarding stall and spin behavior. Complying designs typically have awing with greater angle of attack at the wing root (the part of the wingthat is closest to the fuselage) than at the wing tip, so that the wingroot stalls first, reducing the severity of the wing drop at the stalland possibly also allowing the ailerons to remain somewhat effective incontrolling the aircraft's rolling movements until the stall migratesoutward toward the wing tip. This ideally provides the pilot with someability to control the aircraft in a stalled condition and preclude aspin from developing.

Beyond specifying criteria by which an aircraft must demonstrate certainstall and spin behavior, the Code of Federal Regulations that governsAeronautics and Space, specifically 14 CFR §23.221(a)(2), providescriteria by which an aircraft can be demonstrated to be “spinresistant.” Prior to the implementation of the present invention, noconventionally-configured aircraft has been able to successfullycomplete spin-resistance flight testing and demonstrate spin resistancein accordance with the 14 CFR §23.221(a)(2) standard.

In the 1970s and 1980s, researchers at NASA's Langley Research Centerstudied spin resistance in depth, with a focus on aerodynamiccharacteristics and techniques to make aircraft more resistant to spins.They performed extensive modifications to several aircraft and flewthousands of test flights to determine how changes to the airframe wouldaffect spin characteristics. What they discovered was that small changescould dramatically affect performance during spins. As a result of thestudy aircraft and according to NASA experimenters, aircraft should bedesigned to “give plenty of warning, lots of buffet, very littleroll-off laterally—a long period of telling the pilot, ‘Hey, you'redoing something wrong’.”

One of the key findings of the NASA studies was that a criticalcomponent of spin resistance is controlling the way the wing stalls.Experimenters concluded that having the stall initiate near the root ofthe wing while the outboard panels of the wing continue to fly is idealbecause it prevents the stall from fully developing or “breaking”because the outboard panels are still generating lift. Without a stall,a spin cannot initiate.

Part 23, §23.221 of 14 CFR requires that single-engine airplanes mustdemonstrate recovery from either a one-turn spin if intentional spinswill be prohibited or six-turn spins if intentional spins will beapproved. Even more advantageous than an aircraft able to recover from aspin is an aircraft that is resistant to spin entry. Despite decades ofresearch and an understanding of the interaction between stalls andspins, the design of an aircraft meeting the standards of 14 CFR §23.221has remained a challenge. This and other obstacles of the prior art areaddressed by one or more embodiments of the present invention. That isto say, the present invention provides an aircraft configuration that isspin resistant and in compliance with 14 CFR §23.221(a)(2).

Additional advantages and novel features of this invention shall be setforth in part in the description that follows, and in part will becomeapparent to those skilled in the art upon examination of the followingspecification or may be learned by the practice of the invention. Theadvantages of the invention may be realized and attained by means of theinstrumentalities, combinations, compositions, and methods particularlypointed out in the appended claims.

SUMMARY OF THE INVENTION

Hereafter described in various embodiments and by way of example is aconfiguration and system for rendering an aircraft spin resistant.Resistance of the aircraft to spinning is accomplished by constraining astable stall cell or pattern of stall cells to a wing region adjacent tothe fuselage and distant from the wing tip.

According to one embodiment of the present invention, a wing iscomprised of two contiguous regions. A first region is adjacent to thefuselage and a second region is adjacent to the wing tip. A cuffoperable to form a boundary between the first region and the secondregion is included in one embodiment. The inclusion of this cuffintroduces energy into the airflow such that an aerodynamic fence isestablished on the upper surface of the aircraft and subsequentlyinhibits the progression of the stall cell from the first region towardthe second region.

In accordance with another embodiment, the first region of the wingincludes one or more stall strips, which function as fixed aerodynamicdevices operable to modify the airfoil and, consequently, the airflowaround the airfoil. In an exemplary embodiment, stall strips act inconcert with characteristics of the fuselage and wing to create acondition that, when the aircraft is in a high angle of attackcondition, the airflow interaction between the root and the wing is suchthat the stall is initiated first at the root and progresses outwardtoward the wing tip.

Yet another embodiment of the present invention locates one or morevortex generators on one or more portions of the wing. The vortexgenerators operate to delay airflow separation on the section of thewing adjacent to the wing tip, thus constraining the stall to the wingregion adjacent to the fuselage.

According to yet another embodiment of the present invention, theconfiguration of the wing includes a wing twist, thereby initiating astalled condition first at the root that then progresses outward towardthe wing tip as the angle of attack increases.

The wing configuration of the present invention, in accordance with yetanother embodiment, comprises a forward-swept outboard wing panel, whichallows that portion of the wing to maintain attached airflow sufficientto provide positive control characteristics.

Alone or, preferably, in combination, the aircraft configurationfeatures embodied by the present invention render the aircraft spinresistant by constraining a stable stall cell or pattern of cells to thewing region adjacent to the fuselage, which permits control surfaces ofthe aircraft to remain operational to control the aircraft.

The features and advantages described in this disclosure and in thefollowing detailed description are not all-inclusive. Many additionalfeatures and advantages will be apparent to one of ordinary skill in therelevant art in view of the drawings, specification, and claims hereof.Moreover, it should be noted that the language used in the specificationhas been principally selected for readability and instructional purposesand may not have been selected to delineate or circumscribe theinventive subject matter; reference to the claims is necessary todetermine such inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features and objects of the presentinvention and the manner of attaining them will become more apparent,and the invention itself will be best understood, by reference to thefollowing description of one or more embodiments taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a depiction of aerodynamic conditions present in a spin aswould be known to one of reasonable skill in the relevant art;

FIG. 2 illustrates a planform (outline of an object as viewed fromabove) view of a spin resistant wing configuration and associatedstalled airflow characteristics according to one embodiment of thepresent invention;

FIG. 3 shows an angular implementation of an inboard (toward the centerline) stall strip as associated with one embodiment of a spin resistantconfiguration of the present invention;

FIG. 4 depicts an implementation of dual overlapping stall strips asassociated with one embodiment of a spin resistant configuration of thepresent invention;

FIG. 5 is a combined planform, front and end view of a wing associatedwith one embodiment of a spin resistant configuration of the presentinvention; and

FIG. 6 shows one embodiment of a wing cuff root vortex generator(operable to, for example, delay airflow separation along thewing/fuselage juncture) as associated with one embodiment of a spinresistant configuration of the present invention.

The Figures depict embodiments of the present invention for purposes ofillustration only. One skilled in the art will readily recognize fromthe following discussion that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the invention described herein.

DESCRIPTION OF THE INVENTION

Disclosed hereafter by way of example is a novel configuration ofaerodynamic features that results in an aircraft that is fully spinresistant. According to one embodiment of the present invention, theinteraction of various aerodynamic techniques results in an aircraftthat is resistant to spin entry throughout the flight test envelopestated in the United States Federal Aviation Administration (“FAA”)Regulations. One aspect of the present configuration/combination is acuffed wing design that employs multiple proprietary airfoils across thespan of the wing that controls the progression of a stall to create astabilized stall cell. This discontinuity on the leading edge of thewing delineates the wing into two distinct regions. The outboard (awayfrom the center line) segments of cuffed wings have a different airfoilwith a drooped leading edge as compared to the inboard segments of thewing, which causes the outboard portion of the wing to stall later thanthe inboard portion of the wing as angle of attack increases. Becausethe ailerons are located on the outboard panel that is still lifting,roll control is preserved even after the inboard panel of the wing hasfully stalled. Accordingly, the root sections of the wing possess higherangles of attack across the span and thus stall before the wing tip oroutboard portions of the wing. The cuff also operates as a fence,trapping separated airflow to inboard sections of the wing, while theairflow associated with the outboard sections of the wing remainsattached to the wing. The cuff in this aspect acts as large vortexgenerator whose vortex is shed over the upper surface of the wingtrapping separated airflow to the inboard sections. These and otherfeatures of the present invention form a configuration that is spinresistant.

Many types of airplanes will spin when the pilot simultaneously yaws andstalls the airplane (intentionally or unintentionally). One commonscenario that can lead to an unintentional spin is an uncoordinated turntowards the runway during the landing sequence. A pilot who isovershooting the turn to final approach may be tempted to apply rudderto increase the rate of turn. The result is twofold: the nose of theairplane drops below the horizon and the bank angle increases. Reactingto these unintended changes, the pilot may then begin to pull theelevator control aft (toward the tail of the aircraft, thus increasingthe angle of attack) while applying opposite aileron to decrease thebank angle. Taken to its extreme, this cross-control input can result inan uncoordinated turn with sufficient angle of attack to cause theaircraft to stall. This is called a cross-control stall, and is verydangerous if it happens at low altitude where the pilot has little timeto recover. Add in a little yaw and the loss of control can quicklyevolve into a spin. To avoid this scenario, pilots are taught theimportance of always making coordinated turns and avoiding situationsthat require last minute corrections.

The spinning equation is further complicated by individual aircraftcharacteristics. For example, the likelihood of an aircraft entering aspin is significantly influenced by the position of the center ofgravity. In general terms, the further forward the center of gravity is,the less readily the airplane will spin and the more readily theairplane will recover from a spin. Conversely, the further aft thecenter of gravity is, the more readily the airplane will spin and theless readily the airplane will recover from a spin. In any airplane, theforward and aft limits on center of gravity are carefully defined. Insome airplanes that are approved for intentional spinning, the aft limitat which spins may be attempted is not as far aft as the aft limit forgeneral flying.

One or more embodiments of the present invention present a configurationof an amphibious aircraft that is spin resistant. An amphibious aircraftor amphibian is an aircraft that can take off and land on both land andwater. Amphibians are fixed-wing aircraft that are equipped withretractable wheels, at the expense of extra weight and complexity, plusdiminished range and fuel economy compared to planes designed for eitherland or water only.

While amphibious aircraft exhibit many of the same flightcharacteristics as land-based aircraft, they do possess uniqueaerodynamic features and center of gravity concerns. For example, thelower portion of the aircraft is a watercraft hull and as the aircraftmust obtain speeds sufficient to transition to flight, it must plane ontop of the water. These characteristics cannot only influence the centerof gravity but can also create drag in a high angle of attack situation.

Embodiments of the present invention introduced above are hereafterdescribed in detail with reference to the accompanying Figures. Althoughthe invention has been described and illustrated with a certain degreeof particularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the combinationand arrangement of parts can be resorted to by those skilled in the artwithout departing from the spirit and scope of the invention.

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the present invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary. Likenumbers refer to like elements throughout. In the figures, the sizes ofcertain lines, layers, components, elements or features may beexaggerated for clarity. Accordingly, those of ordinary skill in the artwill recognize that various changes and modifications of the embodimentsdescribed herein can be made without departing from the scope and spiritof the invention. Also, descriptions of well-known functions andconstructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention are provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

By the term substantially it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

The angle of attack of an aircraft is the acute angle between anaircraft's mean wing chord or other defined aircraft longitudinal axisand the direction of the relative free stream wind. A chord line is aline drawn from the trailing edge of the wing to the farthest forwardpoint on the leading edge of the wing.

A stall is a condition in aerodynamics and aviation wherein the angle ofattack increases beyond a certain point such that the lift begins todecrease and drag increases. The angle at which this occurs is calledthe critical angle of attack. This critical angle is dependent upon theprofile of the wing, its planform, its aspect ratio, and other factors,but is typically in the range of 8 to 20 degrees relative to theincoming wind for most subsonic airfoils. The critical angle of attackis the angle of attack on the lift coefficient versus angle-of-attackcurve at which the maximum lift coefficient occurs.

An airfoil is the shape of a wing as seen in a cross section. Theairfoil shape produces aerodynamic forces resulting in lift. Most foilshapes require a positive angle of attack to generate lift, but camberedairfoils can generate lift at zero angle of attack. This “turning” ofthe air in the vicinity of the airfoil creates curved streamlines whichresults in lower pressure on one side and higher pressure on the other.This pressure difference is accompanied by a velocity difference, viaBernoulli's principle, so the resulting flow-field about the airfoil hasa higher average velocity on the upper surface than on the lowersurface.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Thus, for example, reference to “a component surface”includes reference to one or more of such surfaces.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andrelevant art and should not be interpreted in an idealized or overlyformal sense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be also understood that when an element is referred to as being“on,” “attached” to, “connected” to, “coupled” with, “contacting”,“mounted” etc., another element, it can be directly on, attached to,connected to, coupled with or contacting the other element orintervening elements may also be present. In contrast, when an elementis referred to as being, for example, “directly on,” “directly attached”to, “directly connected” to, “directly coupled” with or “directlycontacting” another element, there are no intervening elements present.It will also be appreciated by those of skill in the art that referencesto a structure or feature that is disposed “adjacent” another featuremay have portions that overlap or underlie the adjacent feature.

Spatially relative terms, such as “under,” “below,” “lower,” “over,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of a device in use or operation in addition to theorientation depicted in the figures. For example, if a device in thefigures is inverted, elements described as “under” or “beneath” otherelements or features would then be oriented “over” the other elements orfeatures. Thus, the exemplary term “under” can encompass both anorientation of “over” and “under”. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly. Similarly, the terms“upwardly,” “downwardly,” “vertical,” “horizontal” and the like are usedherein for the purpose of explanation only unless specifically indicatedotherwise.

FIG. 2 shows a high-level plan view depiction of a wing associated withthe spin resistant configuration according to one embodiment of thepresent invention. The wing 200 can be considered to be divided into twosections, an outboard wing section 210 and inboard wing section 220. Thetwo portions of the wing are separated by a wing cuff 215 on the leadingedge located in one embodiment at 50% of the wing semi-span. In otherembodiments the cuff can be positioned farther outboard with locationsranging between 50 and 70% of the wing semi-span. Outboard of the wingcuff 215 the leading edge sweeps backwards slightly while the trailingedge includes a slight forward sweep. The wingtip includes ananhedral/dihedral combination with a rearward extending feature. FIG. 2further includes the on-body airflow characteristics of the wing in afull stall condition. As can be seen, the inboard section 220 presents aclassic reverse airflow or separated airflow phenomena 240 while theoutboard section 210 of the wing maintains attached airflow 250. Thewingtip 230 also experiences minor vortex generation. FIG. 2 illustratesthat the wing 200 in a full stall condition maintains suitable airflowacross control surfaces (the ailerons are located on the outboardsection of the wing) to maintain control of the aircraft. While the wingmay not be able to provide adequate lift to support level flight,portions of the wing maintain attached airflow sufficient to providepositive control characteristics.

As described in more detail below, the wing cuff 215 introduces energyinto the airflow such that an aerodynamic fence is established on theupper surface of the wing. The fence inhibits the progression of thestall, separated airflow, outboard of a line 260 running from the cuff215 to the trailing edge.

Another aspect of one embodiment of the spin resistant design of thepresent invention is the inclusion of a stall strip near the wing root.FIG. 3 shows an angular implementation of a stall strip located on nearthe root 330 of a wing 200 according to one embodiment of the presentinvention. A stall strip is a fixed aerodynamic device employed on afixed-wing aircraft to modify the airfoil. Stall strips are usuallyemployed in pairs, symmetrically on both wings. In rare installations,they are employed as a single strip on one wing to correct aberrantstall behavior. Normally stall strips are employed to generate a stalledcondition near the root of the wing so as to produce turbulent airflowover the tail control surfaces prior to the stall of the entire wing. Insuch a manner, the impending stall is communicated to the pilot.

According to one embodiment of the present invention, one or more stallstrips located on the inboard section of the wing are positioned toinitiate and stabilize an integer number of stall cells on the inboardsection of the wing. In an exemplary embodiment, a wing with an aspectratio of 9 and a wing cuff root located at 60% of the wing semi-span, astall strip is positioned at the mid-span of the inboard section of thewing. In this position, the stall strip is operable to initiate and holda single stall cell on the inboard section of the wing.

In one embodiment of the present invention, stall strips act in concertwith the characteristics of the fuselage and wing to create a conditionthat, when the aircraft is in a high angle of attack condition, theairflow interaction between the root and the wing is such that the stallis initiated first at the root and progresses outward toward the wingtip. As can be seen in FIG. 3, the stall strip 320 is positioned nearthe root 330 of the wing 200 and oriented diagonally downward as seenfrom the front of the aircraft along a span such that the highestportion of the stall strip 320 is at the root 330 above the leading edgeand the lowest portion of the stall strip 320 extends downward in thedirection of the wing tip toward the leading edge. The angularorientation of the stall strip is combined with a wing twist (discussedbelow) that initiates a stalled condition first at the root 330 and thenprogresses outward as the angle of attack is increased.

In another embodiment of the present invention and as shown in FIG. 4, apair of stall strips are positioned on the leading edge of the inboardsection of the wing to control stall progression. Before intersectingthe leading edge of the wing 200 the first or primary stall strip 410concludes and is overlapped 430 by a second stall strip 420. The secondor secondary stall strip 420 begins slightly inboard of the terminationof the primary stall strip 410 and continues outward along the leadingedge of the wing for a predetermined distance before it terminates. Inone embodiment, the secondary stall strip 420 concludes prior toreaching the cuff 215.

In other embodiments of the present invention, the stall strips arealigned with the leading edge of the wing and positioned to form astable stall cell (as shown in FIG. 2) beginning at the fuselage andextending to the cuff. In yet other embodiments, the stall strips arecurved with respect to the leading edge, wing twisted and airfoil variedto control the progression of the stall as the critical angle of attackis reached. As mentioned above with reference to FIG. 2, the vortexgenerated by the cuff 215 also translates outward toward the wing tip asit interacts with separated, reverse flow on the inboard sections 220 ofthe wing 200 and turbulent but remains as attached flow on the outboardsections 210 of the wing 200.

Turning attention in addition to FIG. 5, one can see a combinedplanform, front and end view of a wing associated with one embodiment ofa spin resistant configuration of the present invention. The cuff 215portion of the present invention not only extends the cord of the wing200 forward but also lowers the leading edge at a discrete positionalong the span of the wing 200. The effect of the cuff 215 along withvaried airfoils along the span of the wing 200 is to create anaerodynamic fence via a vortex that traps separated airflow on theinboard section 220 of the wing 200. Accordingly, while the inboardsection 220 of the wing 200 is in a full stall, the airflow associatedwith the outboard section 210 of the wing 200 remains attached. Inanother embodiment, a cuff segment is incorporated into the wing ratherthan a single or unilateral notch as shown in FIG. 5. This type ofsegment cuff produces bilateral opposing voracities as opposed to aunilateral vortex. Moreover, the segmented cuff can be combined with aunilateral or typical cuff so as to render multiple barriers operable tostabilize and control the stall cell.

In yet another embodiment, different wing cuff sections are included inthe profile of the wing's span, each with different configurations. Theintroduction of multiple cuffs produces one or more pronounced andcontrollable fences, trapping the stall cell. Stall strips, as describedabove, are incorporated inboard of the cuff to enhance the separation offlow on the inboard section of the wing at a high angle of attack.

Another aspect of the present invention is the inclusion of washout tothe inboard or outboard wing segments. According to one embodiment, 1.5degrees of washout is included in the wing. For the purpose of thisdescription, washout is defined as wing twist such that the wingincidence decreases from inboard wing stations towards outboardstations. Other embodiments of the present invention include otherdistributions of wing twist. Exemplary embodiments of the presentinvention include a wing twist of 0.5 degrees up to 3 degrees.

Along the span of the wing 200 one configuration aspect of the presentinvention that aids in its ability to be spin resistant is not only thetwist of the wing but the ability to vary the airfoil along the span ofthe wing. FIG. 5 identifies, in one embodiment, five distinct positionsin which the wing 200 exhibits a different airfoil shape and/orconfiguration. In some cases, the airfoil size, that is to say the chordlength and angular orientation, may vary while in other embodiments, theairfoil shape may vary. In the latter case, the wing 200 begins at theroot with a first airfoil cross section 510 that remains constant for aportion of inboard section 220 of wing. At approximately 50% semi-span,the airfoil changes from the inner profile 520 to that of an inner cuffprofile 530. Throughout this section the leading edge and trailing edgeremain the same (i.e. the wing has no twist). At the cuff 215, theleading edge of the airfoil 535 is extended forward while the trailingedge remains coincident. This is the longest chord length of the wing200. From this point to the wingtip, the wing 200 tapers with theleading edge retreating and the trailing edge sweeping forward.Approximately 25% of the distance from the cuff root 215 to the wingtip,a fifth airfoil configuration 540 can be seen. The airfoil and wing 200continues to vary continuously to the wingtip at which a wingtip airfoil550 transitions into an anhedral wing tip 555 with a retreating trailingedge 560.

In other combinations of the present invention the location and amountof wing taper and trailing edge forward sweep can vary so as to maximizethe ability to trap and control the placement of the stall cell near thewing root.

In the one embodiment, a wing cuff is positioned at 50% semi-span withvortex generators, angled at 15 degrees to the aircraft longitudinalaxis and positioned on the outboard wing panel. Each vortex generator isspaced by 3 inches. To energize the airflow and in other embodiments ofthe present invention the vortex generators are spaced between 2 and 4inches with the angle of each generator ranging from 10 to 20 degrees tothe aircraft longitudinal axis. Finally, stall strips are located on theinboard section of the wing, that is, inboard of the cuff, as describedabove. The most inboard stall strip is angled downward at 7 degrees(front view, root to wing tip) and located at 11-25% semi-span withanother stall strip located outboard of the first at positions 24-35%semi-span parallel to the leading edge. As one of reasonable skill inthe relevant art can appreciate the location and angular variation ofthe stall strips can vary. Indeed while the present embodiment presentsa linear stall strip disposed at 7 degrees from the leading edge, otherembodiments can have more or less of an angular orientation based on thewing twist in that particular section and alterations of the effectiveor local angle of attack. For example a wingspan having a morepronounced wing twist may have the stall strips less angled to overallprovide a similar stall initiation phenomena at the root. Also the stallstrip itself may be curvilinear rather than straight based again on thestall initiation and stall cell characteristics. The stall strips arearranged and orientated to make sure that the stall is initiated at theroot and progresses in a controlled manner so that stall cell can becaptured apart from any control surfaces which, under separated flow ofa stall, can be rendered ineffective.

According to one configuration of the present invention, the angle ofincidence is modified along the span of the wing such that at 0-19%semi-span, it is 5 degrees and changes to 2 degrees at 60% semi-span.The wing twist then further reduces to 1 degree at the wing tip (100%semi-span). In this embodiment, the wing cuff is positioned at 60%semi-span and vortex generators, angled at 15 degrees and spaced by 3inches, are located on the outboard wing panel at 10% chord. Finally, asingle stall strip is located at 33-39% wing semi-span which is parallelto the leading edge.

In another embodiment, one or more delta vortex generators attached tothe leading edge of the wing can also be employed to generate a strongvortex at a certain position along the wing span that are operable torestrict the stall to the inboard sections of the wing. Such a vortexgenerator is illustrated, for example in FIG. 6. As shown, the deltavortex generator 630 described is incorporated into the cuff, enhancingthe effectiveness of the cuff for producing a focused vortex. The vortexgenerator 630 extends the leading edge of the outboard section 610overlapping the inboard section 620 of the wing. At high angles ofattack, airflow passes from beneath the outboard section 610 and aroundthe cuff root and vortex generator. The vortex generator 630 energizesthe flow, enhancing the creation of an aerodynamic fence.

Another aspect of the present invention is the inclusion of vortexgenerators on the wing, above the leading edge, outboard of the cuff.The vortex generators add energy to the airflow, reducing boundary layerthickness and enabling the airflow to remain attached to the wing tohigher angle of attack. Another feature of the present invention is notonly the incorporation of a plurality of varied airfoils across the spanof the wing, but a wing twist that places the wing root at a higherangle of attack than the wing tip. As the angle of attack of the wing isincreased, the wing root will experience a higher local angle of attackthan the wing tip and stall first. While the wing twist and theimplementation of various airfoils continually varies from root to tip,there is a discrete change at the cuff creating a fence.

To further enhance the aircraft's resistant to a spin, the tail area andspan are modified in concert with modifications of the wing to enhancestability and spin resistance. To improve longitudinal stability, thespan of the tail is increased and a horizontal tail tip with anincreased sweep is added.

The combinations of features described above with respect to the wingare also enhanced by their relationship to the aircraft fuselage. In oneembodiment of the present invention, the various combinations of airfoilselection, wing twist, stall strips, wing cuff and vortex generators arefashioned in consideration with the interaction of airflow around thefuselage of an amphibious aircraft. In a high wing configuration on topof a fuselage that includes a sponson or sea wing, the airflow over theinboard sections of the wing area is affected by the airflow over thefuselage and sponson or sea wing. The forward position of the sponson orsea wing with respect to the leading edge of the wing acts, in highangle of attack situations, to direct the airflow, reducing the wing'seffective angle of attack and therefore its lift. As a result, the localangle if incidence of the wing in the area of the sponson or seawing canbe increased to make up for the seawing-induced loss of lift, therebypromoting the desirable root-first wing stall progression.

As the Figures illustrate, the aircraft develops a stable and isolatedstall cell confined to the inboard sections of the wing. At full controlinput, a significant portion of the outboard section of the wing,including a significant portion of both ailerons, retain attached flow.The remaining inboard sections of the wing experience either reverse orlateral flow. Despite rolling or yawing the aircraft, the stall cellsremain confined. This confinement of the stall cell promotes spinresistant behavior.

The present invention provides a spin resistant configuration. Bycombining the features of the present invention in a coordinated manner,each individual feature interacts synergistically to create a stablestall cell that is trapped on the inboard portions of the wing. Thestable and trapped stall cell combined with an emmpanage that remainseffective provides the pilot with adequate roll, pitch and yaw control,despite the fact that the wing is in a full stall, to resist entry intoa spin. Indeed flight tests have demonstrated that the stall cell is sowell confined that even with full aft controls and full deflection ofthe rudder, thus inducing yaw into the stall condition, the aircraftremains completely controllable.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative structural and functional designs for asystem and a process for a spin resistant aircraft configuration throughthe disclosed principles herein. Thus, while particular embodiments andapplications have been illustrated and described, it is to be understoodthat the disclosed embodiments are not limited to the preciseconstruction and components disclosed herein. Various modifications,changes and variations, which will be apparent to those skilled in theart, may be made in the arrangement, operation and details of the methodand apparatus disclosed herein without departing from the spirit andscope defined herein.

It will also be understood by those familiar with the art, that theinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. Although the inventionhas been described and illustrated with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the combinationand arrangement of parts can be resorted to by those skilled in the artwithout departing from the spirit and scope of the invention, ashereinafter claimed.

1. A configuration for an aircraft so as to be spin resistant, saidaircraft comprising a fuselage and a wing wherein the wing includes afirst region adjacent to the fuselage and a second region adjacent to awing tip, the first region being contiguous with the second region, andwherein at high angles of attack a stall cell is constrained to remainwithin the first region so as to remain apart from flight controlswithin the second region.
 2. The configuration for an aircraft asdefined in claim 1, wherein the wing includes a cuff operable to form anaerodynamic boundary between the first region and the second region. 3.The configuration for an aircraft as defined in claim 2, wherein thecuff includes a delta vortex generator.
 4. The configuration for anaircraft as defined in claim 1, wherein the first region includes one ormore stall strips associated with a leading edge of the wing.
 5. Theconfiguration for an aircraft as defined in claim 4, wherein at leastone of the one or more stall strips is coupled to the leading edge ofthe wing and angled downward as it extends toward the wing tip.
 6. Theconfiguration for an aircraft as defined in claim 5, wherein at leastone of the one or more stalls strips is coupled to and parallel with theleading edge of the wing.
 7. The configuration for an aircraft asdefined in claim 1, wherein the second region includes vortexgenerators.
 8. The configuration for an aircraft as defined in claim 1,wherein the wing includes a wing twist such that a wing tip angle ofincidence is less than a wing root angle of incidence.
 9. Theconfiguration for an aircraft as defined in claim 8, wherein the wingtwist of the first region is substantially different than the wing twistof the second region.
 10. The configuration for an aircraft as definedin claim 1, wherein the wing tip is swept forward.
 11. The configurationfor an aircraft as defined in claim 1, wherein the aircraft is anamphibious aircraft that includes sponsons.
 12. The configuration for anaircraft as defined in claim 11, wherein at high angles of attack thesponsons reduce an effective angle of attack of the wing near thefuselage.
 13. A system for a spin resistant configuration in anaircraft, the system comprising: a wing having root and a wing tip andwherein the wing includes a first region near the wing root and a secondregion near the wing tip and wherein the first region and the secondregion are contiguous along a contiguous border; and a leading edgediscontinuity operable at high angles of attack to form an aerodynamicfence along the contiguous border isolating a stall cell to the remainwithin the first region apart from any control surfaces in the secondregion.
 14. The system for a spin resistant configuration in an aircraftaccording to claim 13, wherein responsive to a stall cell beingdeveloped within the first region, control surfaces of the aircraftremain operational to control the aircraft.
 15. The system for a spinresistant configuration in an aircraft according to claim 14, whereinaircraft control surfaces are isolated from the stall cell.
 16. Thesystem for a spin resistant configuration in an aircraft according toclaim 13, further comprising a plurality of vortex generators associatedwith the second region.
 17. The system for a spin resistantconfiguration in an aircraft according to claim 13, further comprisingone or more stall strips associated with a leading edge of the wing inthe first region.
 18. The system for a spin resistant configuration inan aircraft according to claim 17, wherein one of the one or more stallsstrips is coupled to the leading edge of the wing and angled downward asit extends toward the wingtip.
 19. The system for a spin resistantconfiguration in an aircraft according to claim 17, wherein one of theone or more stall strips is coupled to and parallel with the leadingedge of the wing.
 20. The system for a spin resistant configuration inan aircraft according to claim 13, wherein the wing includes a wingtwist such that a wing tip angle of incidence is less than a wing rootangle of incidence.
 21. The system for a spin resistant configuration inan aircraft according to claim 20, wherein the wing twist of the firstregion is substantially different than the wing twist of the secondregion.
 22. The system for a spin resistant configuration in an aircraftaccording to claim 13, wherein the aircraft is an amphibious aircrafthaving sponsons and wherein the wing twist at the root is increased dueto an effective angle of attack reduction due to the sponsons.